Manganese dioxide is a known material for use as a cathodic material in batteries. It also is known that it is not suitable for rechargeable batteries. Apparently irreversible structural changes occur in manganese dioxide during discharge which do not permit recharging.
Lithiated manganese oxide made from MnO.sub.2 has been investigated for use in rechargeable batteries. The method of making the lithiated manganese oxide and the manganese dioxide starting material appears to materially affect the effectiveness of the lithiated manganese oxide used in rechargeable batteries. U.S. Pat. Nos. 4,312,930 and 4,246,253 to Hunter describes a lithiated manganese oxide which Hunter says has a particularly effective utility for rechargeable batteries. Each of these Hunter patents is incorporated herein as if fully rewritten.
Making lithiated manganese compounds is not necessarily new. Monchilov and Manev describe making 35 lithiated manganese compounds (see Journal of Power Sources, 41 (1993) 305-314 and Log Batteries, Battery Mater., Vol. 14 (1995), respectively), but do not describe making such compounds from relatively impure compounds which have a high sodium and/or potassium content and making relatively pure lithiated manganese compounds by removing the sodium and/or potassium and replacing those alkali metals with lithium to make a pure lithiated manganese compound.
An object of this invention is to provide a process for making lithiated manganese oxide.
Another object of this invention is to use chemically made manganese dioxide in making the lithiated manganese oxide by the process of the invention.
Yet another object of this invention is to make a pure form of lithiated manganese oxide from the reduction of an alkali metal permanganate or manganate such that the lithiated manganese oxide has a utility that is particularly effective for a cathodic material for rechargeable batteries.
Further objects and advantages of the invention will be found by reference to the following specification.
As used herein, LiMn.sub.2 O.sub.4 means a lithiated manganese oxide with the general formula Li.sub.x Mn.sub.2 O.sub.4 where x is greater than 0, less than about 2 and, in an important aspect is about 1.
As used herein, "amorphous manganese dioxide" means a manganese dioxide which does not have a substantially identifiable crystal structure as determined by x-ray diffractometry.
As used herein, "delta manganese dioxide" means a manganese dioxide which does not have a single crystal structure which dominates to provide a manganese dioxide with at least one identifiable crystal structure. Delta manganese dioxide is often described as having the following general formula M.sub.2 O.4MnO.sub.2 where M is an alkali metal cation.
As used herein, "reducing permanganate" means taking manganese (VII) to manganese (III or IV).
As used herein, "substantially all Mn IV" means at least about 90 weight percent Mn IV and not more than about 10 weight percent Mn III.